The problem of attaching a long handle to an implement head is one of long standing. Classically one finds a long, solid wooden handle mated with an iron or steel end formed in the shape of one kind of tool head or another. The metal tool head typically comprises a socket for receiving one end of the handle. The difficulty is in providing an attachment means that is tight, and will remain tight over years of use. In the past the handles have been given tapered ends, and the heads have sometimes been heated and cooled to fit on them. Often a nail or screw is driven transversely through the socket into the handle to prevent rotation. Particularly common with brooms is the device of a coarsely threaded socket in the wooden broom head transverse member suited to engage an equally coarsely threaded handle end. Theses sockets have been found frequently to be unsatisfactory.
In some cases glues have been used in these sockets to take up the mismatch in fit between the handle and the socket. Often the insertion of the handle into the socket causes the glue to be pushed or squeezed out of the joint, and so not to form the uniform bond that had been desired.
A related problem involves the use of one handle with several different tools. As noted in U.S. Pat. No. 4,466,377 to Kolb et al. it is often desirable to reduce the storage space required for a set of garden implements and use of a common handle for several tools is therefore advantageous. Further, one may wish to replace either the head or the handle, rather than having to discard both if one has worn out.
Yet a further related problem concerns the use of hollow tubular implement handles. Traditional wooden tool handles are usually solid. More recently tool handles have been made from moderately thin walled steel and aluminum tubing, from plastic, and from laid up fibreglass. These tubular members combine the advantages of strength and lightness.
Tubular members present two different challenges to the designer. First, transverse holes in tubular members are particularly troublesome stress concentration sites. After a period of working a handle tends to loosen, and then the transverse nail, screw, or rivet tends to work in the hole, tearing or deforming the tube. In composites structures the laminate in the region of the hole is soon destroyed. Second, while it is recognized that threaded connections are generally preferred over merely a smooth, tapered fit, it may be difficult to thread thin walled tube stock satisfactorily, and doubly so with composite thin walled tube stock. Even when threaded the region of the tube adjacent the socket is a zone of stress concentration and failure. It is difficult, and expensive to pre-mold threads into tube stock, and the threads so formed may be unsatisfactory.
In U.S. Pat. No. 4,466,377 to Kolb et al., one finds a bayonet-like implement prong to locate within a female socket. The prong has a transverse hole and is held in place by a releasable leaf spring. It is the leaf-spring itself which prevents the prong from disengaging from the socket when the handle is being used to pull an object, such as might occur while raking leaves.
In U.S. Pat. No. 5,161,278 to Tomm one finds that the long-standing broom handle problem is addressed with a multipart threaded-socket and handle system. This system includes a locking ring which is captured between a lock nut and the, presumably, wooden, transverse head member. The tight retention of the tool head depends on the hand-tightened locknut remaining tight, and on some amount of deformation of the wooden tool head as the teeth of the locking ring dig in. This deformation may not be desired.
Therefore, there has been a long felt need for an attachment means for attaching a handle to a tool head that may be well tightened, which has a locking means to prevent the head from turning about the handle, or wobbling during use, and which allows for removal of the handle from the head.